[Tutor] Function assignment (was: Re: Function type?) [example:new.instancemethod]

[Zak Arntson]

> On Wed, 11 Jun 2003, Jeff Shannon wrote:
>
> [warning: the following is very dynamic code; do we really want to do
> this?  *grin*]

Of course! Actually, it's good to discuss that. A lot of times we'll write
hefty code, not realizing it isn't needed (and by "we" I mean "me"). After
this big exercise, I may decide NOT to incorporate dynamically-added
functions. But it's still a cool thing to know.

Using your way, I concocted this class:
###
import new

class PyFictObject:
    def attach(self, func, name=None):
        setattr(self,
                name or func.__name__,
                new.instancemethod(func, self, PyFictObject))
    def msg(self, name, message):
        def f(self, message):
            return message
        self.attach(f, name)

# sample usage

pipe = PyFictobject()

# First, use attach to add a function.
def desc(self):
    return "Here's a pipeDesc function! It could be more complicated."
pipe.attach(desc)

# Second, use msg to add a "string" which is really a function
pipe.msg('name', 'big green pipe')

###

Unfortunately, the msg function isn't working at all. I can't figure it out!

>
> The only reason we're going through that dynamic route is because Zak's
> doing it that way.  *grin* But perhaps the simpler approach better
> mimics what Inform does?
<SNIP>
> Here's a few questions I have: in Inform, do the two definitions above
> create templates for all kinds of pipes, or do they make single object
> instances?

The two definitions make a pair of object instances. Their class is Object.

>  Does Inform allow the addition/attachment of different
> attributes to an 'Object' (like 'name' or 'description') after it's been
> created?

No. All properties (methods, lists, variables) and attributes (logicals)
must be defined _for all instances of every class_. The equivalent Python
code (if you defined things in advance) would be (well, the following code
is actually buggy, but you can see what I'm seeing):

###
class GameObject:
   def name(self): pass    #stub
   def description(self): pass     #stub
   # OTHER STUFF, LIKE in_player METHOD

pipe = GameObject()
def name (self):
   return 'pipe'
attach(pipe, name, 'name')
def description (self):
   if self.in_player():
      return 'pipe in your hand!'
   return 'pipe on the floor.'
attach(pipe, name, 'name')

# pipe2 excluded, but you get the idea

###

-- 
Zak Arntson
www.harlekin-maus.com - Games - Lots of 'em